All about the powerful J58 engine and its many achievements
There are engines and there are engines! The Pratt & Whitney J58 is an American afterburning turbojet engine that powered the Lockheed A-12, the YF-12 interceptor, and the SR-71 Blackbird reconnaissance as well as the SR-71B trainer aircraft. It features a unique compressor bleed to the afterburner that gives it increased thrust at high speeds.
The first engine designed to operate for extended periods using its afterburner
“The J58 engine was developed in the late 1950s by Pratt & Whitney Aircraft Division of United Aircraft Corp. to meet a U.S. Navy requirement. It was designed to operate at speeds of Mach 3+ and at altitudes of more than 80,000 feet. The J58 was the first engine designed to operate for extended periods using its afterburner, and it was the first engine to be flight-qualified at Mach 3 for the U.S. Air Force,” stated the National Museum of the United States Air Force.
The engine requires two modes of operation to take it from the ground to 2,000 mph at altitude. In fact, the way the engine functioned at cruise led it to be defined as "acting like a turboramjet."
The engine was used by both the CIA and USAF over many years and was later optimized for use in NASA’s experimental work which required more thrust to deal with higher aircraft drag.
The engine’s development involved some of the most challenging metallurgical development problems experienced by Pratt & Whitney Aircraft thus far. This is because it featured components operating at unprecedented temperatures and levels of stress and durability.
This saw the development of new manufacturing techniques, new alloys, and new surface coatings all engineered to protect the engine’s many components.
“Pratt & Whitney designed this engine for continuous operation at high Mach number flight with compressor inlet temperatures above 400 degrees C (750 degrees F). Development began about 1958, and production began in 1964,” explained the National Air and Space Museum on its site.
“The J58 had a single-shaft rotor design, with an 8.8:1 pressure ratio compressor, which incorporated a unique compressor bleed bypass at high Mach number. When opened, bypass valves bled air from the fourth stage, and six ducts routed it around the compressor rear stages, combustor, and turbine. The bleed air re-entered the turbine exhaust around the front of the afterburner where it was used for increased thrust and cooling. The main fuel control scheduled the transition to bypass operation as a function of compressor inlet temperature and engine speed. For extreme high-altitude and high-speed environment operation, the engine required special fuel and oil.”
The engine represents the miracles that can happen when engineering and science come together to push forward the boundaries of speed and efficiency. Today, the engine has been used in many crafts and has served to increase their viability and ability to thrive under extreme conditions. In July 1976, J58 engines powered an SR-71 to a world altitude record of 85,069 feet and another SR-71 to a world speed record of 2,193 mph. Now that’s a noteworthy achievement!